Enable/Disable Trackpad on New MacBook

Update Aug 20th, 2011.
In Lion, you can still find it in Universal Access -> Mouse & Trackpad. Just one more click on Trackpad Options... as below.
Update Oct 7th, 2009.
The option appears in Universal Access -> Mouse & Trackpad. I remember that I have checked here before 10.6, this must be new in Snow Leopard. Anyway, it's much easier now.
Thanks to Mary pointed this out in comment.
I moved the OS X Leopard from the old MacBook to new MacBook and I found that the setting in the Trackpad was missing. I set to "Ignore trackpad when mouse is present" before. After moving the hard disk to new MacBook and reinstall the system without erasing old data, I could not change the setting anymore.
I searched the official MacBook forum and got the solution for that:
Open Terminal and input following command:
defaults write -g com.apple.mouse.ignoreTrackpadIfMousePresent 0
1: Disable Trackpad (Ignore)
0: Enable Trackpad
Log out and log in again then it will take effort.
Thanks brian_b provided the solution via Apple Support Discussion

Hello, faby
For I’m using MacBook aluminum, I’m not sure if it works in iBook. You may have a try as following:
defaults write -g com.apple.trackpad.scrollBehavior 2
0 Disable
1 Use two fingers to scroll
2 Allow horizontal scroll
Good luck!

David Windsor responded:

I want to thank you for a very informative post. I have been having issues with the trackpad on my MBP. I wanted to disable the trackpad until I could find a resolution to my problem. Your post really helped me out a lot. I would never have figured out where the option was to disable the trackpad! Thanks again!!

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cori responded:

Tkjune, I looked all over for this option and couldn’t find it. Then I found your post and realized they moved it under Universal Access. I think it would have been OK to put it in under Trackpad, and Mouse sections as well. They put the mouse stuff under Trackpad so go figure 😛 Anyways, thanks for the tip!

Diego Peña responded:

Bente responded:

Mohsen Jafari Malek responded:

@Tkjune; Thank you! It’s really useful, I have a MacBook (late 2007) and the hand rest on right side of it is broken! sometimes my trackpad make some problems because of this! NOW when I disable the trackpad it’s gone!
thank you again! 😉 good luck

Bryan responded:

YAYYY – thanks for teaching me about universal access and being able to shut down trackpad while I have a mouse attached!

I was about to go nutzo. My damn trackpad would click when my palm put too much pressure anywhere RIGHT of the trackpad – WAY away from where it should be clicking. I could even reproduce it by pushing with one finger, like in the middle of the space, in line with the up and down arrows. Crazy, man, crazy.

I’ve got the same problem everyone else has had – I can’t disable the trackpad when a mouse is installed. I’ve checked in Hardware>Keyboard and Mouse, Hardware>Trackpad and System>Universal Access>Mouse & Trackpad and nowhere does and option to Ignore trackpad when mouse is present. Universal Access has Ignore trackpad when mouse keys is on but not when mouse is present. I have Mac OS X, Version 10.5.8.